1. Field of the Invention
The present invention relates to a gray cast iron member.
2. Description of the Related Art
Gray cast iron, which has been disclosed for example in JP 2002-105581 A and JP 2003-247014 A, is excellent in productivity and wear resistance but is low in tensile strength so that its application to structural parts is much limitative. In order to overcome this and to facilitate applications of gray cast iron to structural parts such as locker arms for actuation of suction and discharge vales in a vehicle engine, it has been practiced to highly strengthen the gray cast iron. Such highly strengthened gray cast iron may be fabricated, for example, through (1) low carbon or inoculation technique or (2) addition of alloys.
Of such highly strengthened gray cast iron, the gray cast iron of type (1) is disadvantageous in cost and productivity since steel scrap as much as 40–100% is used when raw material is to be molten, and casting is conducted through recarburization. In the gray cast iron of type (2), char tends to be separated out at thin portions and such thin portions with char separated out have characteristics substantially different from those required originally, which disadvantageously limits tensile strength of ordinary gray cast iron to be of the order of at most 350 MPa.
The present invention was made in view of the above and has its object to provide a gray cast iron member which has no substantial increase in hardness, is excellent in wear resistance, has tensile strength of 400 MPa or more and has high productivity.